The present invention relates to brushes and in particular to electrostatic charging and cleaning brushes for use in electrostatographic imaging systems.
In an electrostatographic reproducing apparatus commonly used today, a photoconductive insulating member may be charged to a suitable potential, thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image areas contained within the original document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with a developing powder referred to in the art as toner. During development the toner particles are attracted from the carrier particles by the charge pattern of the image areas on the photoconductive insulating area to form a powder image on the photoconductive area. This image may be subsequently transferred to a support surface such as copy paper to which it may be permanently affixed by heating or by the application of pressure. Following transfer of the toner image to the support surface the photoconductive insulating surface may be discharged and cleaned of residual toner to prepare for the next imaging cycle.
Both the step of charging the imaging member and the step of cleaning the imaging member of residual toner following transfer of the image to the copy sheet have been suggested to be accomplished by the use of rotating fiber brushes. For example, Japanese Patent Publication No. 56-139156(A) published Aug. 18, 1983 shows two rotating brushes to uniformly charge a photoreceptor, Japanese Patent Publication No. 57-49965(A), published Mar. 24, 1982 describes a friction charger for a photosensitive medium. Japanese Patent Publication No. 57-49964(A) published Mar. 24, 1982 illustrates brush charging with a conductive liquid to prevent variations in charging. Japanese Patent Publication No. 57-46265(A), published Mar. 16, 1982, describes a carbon containing charging brush. Japanese Patent Publication No. 58-14908(A), published Sept. 5, 1983, illustrates a conductive brush charger and cleaner.
The above referenced Seanor application, together with U.S. Pat. No. 4,494,863 to John R. Laing, issued Jan. 22, 1985, describes electrostatically biased brushes used as cleaners in an electrostatographic reproducing apparatus.
The problem frequently encountered with brushes used in electrostatic charging and cleaning is that their performance latitude can be severely limited by the presence of seam gaps or slight void areas interspacing the spiral wound fabric in the brush. Since it is desirable to use these rotatably mounted charging and cleaning brushes at the lowest possible rotational speeds to reduce toner emissions, to reduce brush and imaging surface wear, and to minimize the energy required to rotate the brushes, frequently non-uniform or streaky charging and cleaning performance is apparent due to seams, or void areas between the spiral windings of the fabric. While it is recognized that charging and cleaning efficiency may be improved by rotating the brushes at an increased speed, thereby masking the presence of seam gaps, the benefits alluded to above are thereby lost In addition this contributes to increased brush speeds, higher emitted noise, more expensive bearings and enhanced structural support for the apparatus.
Seam gaps interspacing the spiral wound fabric occur frequently in traditional brush manufacturing processes wherein the seam interface cannot be precisely nor reliably controlled. Several factors contribute to this shortfall. First, since loss of conductive fibers from these brushes can contaminate sensitive electrical devices within an electrostatographic copier, a narrow flange of backing material must be woven or knitted along each edge of the strips of pile fabric during the fabric manufacturing process. These flanges permit slitting of the fabric by ultrasonics, or hot knife, or other means that melts and seals the lengthwise cut edges of the pile strips without allowing any cutting or severing of conductive pile fibers or regions where conductive pile fibers connect with the backing fabric. Thus, integrity of the conductive fibers themselves and within the backing is preserved. In practice however, the width of the flange itself cannot be precisely controlled. Therefore, in the case where two sections of pile fabric having relatively wide flanges are abutted during spiral winding onto the brush core, pile fiberless areas result in one type of seam gap.
A second type of seam gap is experienced during large scale brush manufacture where a mechanized spiral winding apparatus is used to wind the strip of pile fabric in a spiral configuration onto a cylindrical core. Typically, these machines cannot precisely abut the strips without seams or overlap. In the case where overlap must be avoided, a compromise is thusly made towards somewhat wider seam gaps.
A third type of seam gap can be identified as caused by variations in the width of the fabric strips themselves. Typically, the fabric strips are backcoated with a conductive latex after which heat is applied to assist in drying the latex coating. Some non-uniform shrinkage can occur during this coating and drying process. In the case where two relatively narrow sections of fabric strip are abutted during a constant pitch spiral winding process, a seam gap can result.